Predation Flashcards
What effect does predation have on sp 1 vs sp 2?
Sp1- Negative
Sp2- Positive
Whats predation?
-Interaction between consumers (predators) and resources (victims, prey)
What increases predator population growth?
Reduction in prey population
What does the Lotka-Volterra predator-prey model assume? Is it realistic? What effect of predators is it trying to see?
- Specialist predator on single prey (narrow range of conditions)
- Victim pop is limited by predators
- Predator/prey regulate one another’s populations
- No; As soon as predator feeds on prey using energy to go into reproduction
- How much predator population will decrease per capita growth rate of prey
What does alpha stand for?
Every time predator captures a victim- how many times will they be successful?
-Capture efficiency
How does the equilibrium for V depends on P?
Only few predators wont be able to control prey population- prey pop increase and vice versa
What does predator growth depend on?
Prey abundance
Whats neutral stability?
Will cycle with different amplitude if perturbed (unsettled)
1 way to increase realism of Lotka-Volterra model? What does the victim isocline produce? Why more stable?
- Victim carrying capacity
- Density Dependence
- Can run out of resources
- Damped oscillations
- Victim pop is regulated by another factor besides predator
Whats a basic functional response?
- Rate of victim capture by predator as a function of victim abundance
- Type I
- Increases realism
Explain Type II functional response. What does it arise from?
-At high prey
predators get full
time needed to consume victims (handling time)
- Handling time- Time needed to “handle” prey reduces overall consumption rate
Explain Type III functional response.
-At high prey: predators get full
time needed to consume victims (handling time)
-At low prey: Poor search image, Prey refugia (hiding places), and Switch to other prey
What is type I fractional response?
Linear horizontal line
What is type II fractional response?
- Fractional consumption rate decreases with population increase
- Predator is having smaller impact on victims pop growth
- More realistic model for how quick predators can feed upon victims.
- More victims- predators consume less share of pop; less effective in regulating size of victims.
What is type III fractional response?
Fraction consumed increase initially- but will plateau- victims go up more but smaller impact
What does the victim isocline with a type II functional response produce?
- Increasing unstable oscillations
- Not stable because predator is less effective at regulating victim pop
Whats the Rosenzweig-Macarthur model?
- Combines prey density-dependence with Type II predator functional response
- Simplest “realistic” model of predator-prey systems
Rosenzweig-Macarthur model victims isocline. What does the stability depend on?
- Parabola
- Predator isocline
Whats the Paradox of Enrichment?
- As CC increases, victim pop destabilizes because predator is more responsible for its suppression
- Lower CC- stable
- Increase CC- limit cycles
- very high cc- intersect predator isoline; unstable pop; 1 or 2 species will go extinct
Why might predator isocline not be vertical?
Predator interference
→ must defend territory or fight other predators
Predator density-dependence
→ regulated by other factors when excess victims
Alternative prey sources
→ switch to other prey when few victims
Victims have density-dependent effects
→ stable ratio of predators to victims
3 considerations for each potential item in the optimal foraging theory.
- Energy (Ei) = net calories obtained
- Encounter rate (λi) = # found per unit search time
- Handling time (hi) = time needed to consume
Diet preference is based on?
The profitability of each item:
-Profitability = Ei/hi
(rate of energy gain once prey has been located)
- The most profitable items should always be included in diet
- Less profitable items may or may not be included
What is energy intake?
E/T
Should profitability or energy intake be more?
Profitability
What are some predictions from optimal foraging?
Inclusion of less-preferred items
does not depend on their encounter rate
does depend on encounter rates of more-preferred items
Foragers should broaden their diet as preferred items become less abundant
How to determine rate of food depletion?
Can use functional response to predict rate of food depletion (assume a single consumer)
Intake rate decreases over time
How to decide when to relocate?
-Cost of travel time not spent foraging
-Weighed against higher intake rate of new patch
-Maximize-
Food consumed/ foraging time + travel time
How do travel time and food availability affect foraging decisions?
- Give-up times: time spent in patch before moving
2. Give-up density: amount of food remaining upon leaving
How do longer travel times affect give up times and densities?
- increased give-up times
- decreased give-up densities
How do more food in patches affect give up times and densities?
- increased give-up times
- increased give-up densities
Whats the marginal value theorem?
- Describes behaviour in a patchy system where food and resources vary in resource density and are some distance apart.
- Helps predict the optimum time for the organism to stay in the patch gathering resources before moving on
